DE69715222T2 - INGREDIENTS OF ABSORBENT ARTICLES WITH IMPROVED LIQUID CAPACITY - Google Patents

Description

The present invention relates to an absorbent article having a liquid-permeable outer cover layer arranged on a first surface of the article, a liquid-impermeable cover layer arranged on a second surface of the article and an absorbent body enclosed between the two cover layers, wherein the absorbent body comprises a liquid acquisition layer and, arranged substantially in the same plane therewith, a liquid receiving or liquid acquisition space comprising at least one void or at least one region of lower density than the acquisition layer adjacent to the space, and where the liquid acquisition layer comprises a material which, when wetted, increases in size in a direction (z-direction) generally perpendicular to the first surface of the article.

A problem with previously known absorbent articles, such as diapers, pants-type diapers or training diapers, incontinence guards, sanitary napkins and similar articles intended to repeatedly take up and absorb body fluid discharged by a user, is that the rate at which fluid is able to penetrate the article is greatly reduced with each repeated occurrence of wetting. This problem is particularly evident in diapers and incontinence guards for children and adults, since the article must be able to take up and absorb a comparatively large volume of fluid discharged in the course of only a few seconds. It is therefore not It is unusual, particularly after the article has been wetted for the first time, for liquid which is not immediately absorbed into the article to instead flow across the surface of the article and over the edges. Such body fluid leaks are of course highly undesirable because they contaminate and soil, among other things, clothing, bedding and mattresses, sometimes to the point of destruction.

The reason why the rate of body fluid capture decreases with repeated wetting of the article is because the absorbent body of the article is temporarily saturated with body fluid within a limited area around the point where the surface of the article is first hit by the body fluid, the so-called main wetting point. Typically, the absorbent articles comprise one or more layers of hydrophilic fibers, such as cellulose fluff pulp, and often also a highly absorbent hydrocolloidal material, so-called superabsorbents. The liquid transport in such material is comparatively slow, as it depends primarily on capillary forces in the voids that exist between fibers, as well as between particles in the absorbent body of the article. Liquid is transported within the hydrocolloidal material by diffusion, which is a slower process than that produced by capillary forces. Thus, liquid remains in the main wet area of the article for a comparatively long period of time, and is then only gradually transported to surrounding parts of the absorbent body of the article.

In recent years, the problem has been addressed by developing absorbent bodies that have been successfully compressed to larger dimensions, with with the aim of reducing packaging volume and for reasons of transport, storage and the environment.

It is known to direct the transport of liquid from the main wet area to those parts of the absorbent body where absorbent material that has not yet been used is arranged, by providing the article with liquid transport means in the form of compressed patterns, e.g. compressed strips, which distribute the liquid in the longitudinal direction of the article. An article comprising such compressed strips is known from PCT/SE94/00835. Liquid transport in the article is primarily achieved as a result of differences in the capillary forces between the compressed strips and the surrounding material. Although a certain positive effect is obtained in this way, in the form of a directed flow of liquid into the absorbent body, the rate at which the liquid is transported in the article is far too slow in relation to the rate at which body fluid is drained to the article. There is thus a risk that liquid will not be absorbed quickly enough and instead will run along a surface of the article and leak over the edges of it. This risk is particularly applicable to products intended for urine absorption, such as diapers and incontinence guards, which often have to deal with large volumes of liquid being released in a relatively short period of time. Furthermore, strong compression of an article makes the article stiff and gives it parts that are not easily yielding, making the article less yielding and making it less likely for the article to mould itself to the shape of the wearer's body when worn.

The capacity of an absorbent article to absorb and retain large volumes of body fluid can be further enhanced by creating different types of fluid-absorbing cavities or shells in the article.

US 3,889,679 describes a diaper having several circular openings arranged through the absorbent body of the diaper. However, since wetting of a diaper takes place within a limited area of the diaper, the main wetting area, only those openings arranged closest to this area can initially be used to absorb body fluid. These openings quickly fill with fluid, which is gradually drained away from the openings by the surrounding absorbent material through the suction effect created by the capillary forces between the fibers in the absorbent material. This is a slow process, as previously mentioned, and there is a significant risk that fluid will still remain in the openings when fluid is drained at the next wetting occasion. The absorbent material located closest to the main wetting area of the diaper will gradually become saturated with body fluid and will then lose essentially all ability to drain fluid from the openings. Another problem with this absorbent body is that it is primarily made of a material that collapses when wetted and thus essentially loses its three-dimensional shape. Consequently, the void space available in the absorbent body for the capture of fluid is practically nonexistent after the first wetting.

US 4,560,372 describes an absorbent body comprising a flexible fiber layer and a layer of hydrophilic fibers that have been compressed, slit and then pulled apart to form openings. The absorbent body further comprises 20-60% superabsorbent material. As a result of this high proportion of superabsorbent material, the material swells in both the z and xy directions when wetted, i.e. the material swells into the openings at the same time as it swells in the thickness direction of the material, thereby reducing the area of the openings considerably after wetting.

Swedish patent application number 9304321-4 describes an absorbent body for absorbent articles, such as diapers, incontinence protectors and sanitary napkins, provided with a liquid acquisition part in the form of a drainage opening, which is arranged substantially opposite to the intended main wet area of the absorbent body, and extends downwards in and through a liquid storage part of the absorbent body. The drainage opening is in liquid communication with a liquid distribution layer arranged below a liquid storage layer and has a larger effective average pore size than the surrounding liquid storage part.

An absorption body of this type acts efficiently in terms of receiving a first volume of liquid and even a subsequent volume of liquid if the time between liquid discharges is sufficient to allow the opening to empty itself of liquid between the occasions when liquid is discharged. The absorption body according to Swedish patent application number 9304321-4 is further dependent on capillary forces in discharging liquid from the opening. Consequently, the liquid collection opening is gradually emptied as liquid flows from the larger pores in the opening to the finer pores in the surrounding absorption material is transported. There is also a risk that the opening is too small to accommodate large volumes of liquid and is therefore overfilled.

The prior publications WO 87/01914; US 4,333,462; US 4,333,463; US 4,333,464; US 4,413,996; EP 0,124,365; GB 2,156,681; US 4,643,727 and EP 5,528,567 also describe similar products which are provided with liquid-absorbing and collecting cavities or shells.

However, there still remains a significant need for an absorbent article that can be repeatedly wetted with a high fluid acquisition rate, including subsequent wettings.

Our previous invention, described in copending PCT application WO96/20670, relates to an absorbent article comprising a liquid-permeable outer layer disposed on a first surface of the article, a liquid-impermeable outer layer disposed on a second surface of the article, and an absorbent body enclosed between the two cover layers and having a body fluid receiving space comprising at least one void or region of lower density than the density of a part of the absorbent body disposed adjacent to the receiving space and extending generally in the same plane as the latter, the article being characterized in that the receiving space is disposed in a storage layer in the absorbent body; and in that portions of the storage layer adjacent to the receiving space comprise a material that, when wetted, increases in volume in a direction (z-direction) generally perpendicular to the first surface of the article, whereby the size of the receiving space also increases in that direction as a result of the article being wetted.

However, the sole requirement that the material of the storage layer adjacent to the receiving space should increase its volume in the z-direction does not always ensure a sufficient volume increase of the liquid receiving space and therefore does not necessarily lead to improved liquid acquisition properties under repeated wetting under all circumstances.

It is therefore an object of the present invention to achieve an absorbent article of the type defined in the introduction which has substantially improved liquid acquisition properties during repeated wettings.

According to the invention, an article of the type mentioned in the introduction has been created which offers a solution to this problem. The article according to the invention is primarily characterized in that, when wetted, the material present in the acquisition layer has a comparatively small expansion in a direction (xy direction) substantially parallel to the first surface of the article such that the volume of the liquid acquisition space increases by at least 100%, preferably at least 200%, more preferably 400% and most preferably at least 900% when the material of the acquisition layer is wetted with a 0.9% NaCl solution until manufacture.

An expansion of the material in the xy direction is preferably not greater than such that it results in a reduction in the area of the liquid detection space in the xy direction by at most 25%, preferably at most 20%, and most preferably at most 10% when the material is wetted.

An expansion of the material in the z-direction is preferably at least 100%, preferably at least 200%, more preferably at least 400%, and most preferably at least 900%.

A storage layer is preferably arranged in fluid communication with the liquid acquisition layer on that side of the layer which is proximal to the liquid-impermeable outer cover layer. The storage layer preferably comprises a material with good fluid holding properties, such as cellulose fibers in combination with superabsorbent material, tissue laminates with superabsorbent material or absorbent foam material.

According to a preferred embodiment, a distribution layer is arranged in liquid communication with the absorption layer, either between the layer and the storage layer or between the storage layer and the liquid-impermeable outer cover layer. The distribution layer preferably comprises a material that has good liquid distribution properties, such as compressed cellulose pulp, a fiber mat or wadding made of synthetic or natural fibers, or an open-cell foam material.

Between the liquid-permeable outer shell layer and the acquisition layer, there is preferably arranged a liquid transport layer comprising a material capable of rapidly absorbing liquid and rapidly transferring the liquid to the underlying layer. This transport layer can consist of a slightly compressed cellulose fluff layer of mechanical, thermomechanical, chemithermomechanical pulp (CTMP) - cellulose fibres which have been chemically stiffened or cross-bonded, of a fibre mat or wadding of synthetic or natural fibers or absorbent foam material.

According to one embodiment of the invention, the liquid sensing space of one or more apertures or regions of lower density than the density of the surrounding material in the sensing layer extends through at least a portion of the thickness of the sensing layer.

According to a further embodiment, the acquisition layer consists of at least two separate material bodies in the form of columnar spacers extending generally perpendicularly between two further material layers in the article and together with the material layers defining a coherent acquisition space between the material layers. According to a further embodiment, the acquisition space consists of at least one channel-like cavity extending in the longitudinal direction of the article.

According to yet another embodiment of the invention, the detection layer is formed by a material web which is divided in the longitudinal direction of the web by a wavy curve, the web parts being offset with respect to each other in the plane of the web, and at least in the longitudinal direction thereof such that the web parts define the detection space between in the plane of the material web. A wavy curve is understood to mean a curve of any shape, such as a sinusoidal shape, a sawtooth shape, a square wave shape, etc. The amplitude of the waves and their lengths can vary along the curve. The waves can extend along a straight, curved or wavy line.

A particularly suitable material for use in an article according to the invention for forming the Acquisition layer surrounding the liquid acquisition space consists of pulp fibers from mechanical, thermomechanical or chemomechanical (CTMP) pulp and/or chemical pulp fibers that have been chemically stiffened or cross-bonded, the fibers being formed into a web having a basis weight of 30-2000 g/m², preferably 50-1500 g/m² and more preferably 100-1000 g/m², and compressed to a density of between 0.2-1.2 g/cm³, preferably 0.25-1.0 g/cm³ and most preferably 0.3-0.9 g/cm³. The pulp fibers may consist of fluff dried fibers in a conventional manner that have been dry formed into a web and incorporated into the article without defibration and fluff formation. Such a material is described in WO94/10956. The material may have been compressed to a first density of between 0.2-1.2 g/cm³, and subsequently mechanically softened to a density less than the initial density and delaminated to form a plurality of not completely separated thin fiber layers having a density corresponding to the first density.

Another conceivable acquisition layer is formed from a material layer having a first thickness and with compliant material, the layer having been compressed to a second thickness perpendicular to a plane through the layer, and in its compressed state having been bonded to a binding agent that is soluble in body fluid, the bonding of the material layer disappearing when the layer is wetted and the acquisition layer at least partially returning to its first thickness. Such an acquisition layer can be formed, for example, from a compressed foam material that expands in its thickness direction when wetted, or by a compressed fiber layer that consists at least partially of fibers that have a certain compliance in a wet state.

According to a further embodiment of the invention, the proportion of the volume of the acquisition layer consisting of the liquid acquisition space is greatest within the main wetness area of the article, i.e. the area in the article that is intended to be wetted first by body fluid. The acquisition layer volume occupied by the liquid acquisition space can thereby decrease in a direction away from the main wetness area.

Because the volume of the liquid acquisition space of the inventive article expands simultaneously with the extent to which the article is wetted by body fluid, the article is able to maintain a high liquid acquisition rate throughout the entire period during which the article is worn. Unlike previously known articles, there is no dramatic reduction in the acquisition rate when repeated wetting occurs, since a new liquid acquisition space is continuously created. In advantageous cases, the inventive article can maintain substantially the same liquid acquisition rate after several wetting events. In particularly advantageous cases, the acquisition rate can even increase after the first wetting event.

In order to achieve the full effect of the expanding liquid acquisition space in the absorbent body according to the invention, it is essential that at least the material layer arranged in contact with the side of the storage layer which is proximal to the liquid-permeable surface of the article has a resilience and stiffness in both a wet and a dry state which prevents the material layer from collapsing and collapsing into the Fluid collection space falls, since otherwise a large part of the space available for further fluid collection would be lost.

Those voids, low density regions, channels or the like which together form the liquid acquisition space of the article preferably have no dimension in the plane of the acquisition layer which exceeds 35 mm, and preferably does not exceed 20 mm. By this is meant that the extent of such void, low density region, channel or the like cannot accommodate within its area a circle having a diameter greater than 35 mm, and preferably not greater than 20 mm, anywhere in the plane of the acquisition layer. Because of the compliance of the material, it is difficult to prevent surrounding layers of material from expanding towards the liquid acquisition space with dimensions greater than those mentioned above, thereby reducing the space. Absorbent articles mold and curve in conformity to the wearer's body during use. The layers of material which are proximal to the wearer tend to curve and bulge into the acquisition space. This bulging generally increases when the material in the shell layer is wet and is even more pronounced when the storage layer has large voids. Of course, this bulging can be reduced by using a stiffer layer of material closest to the storage layer, but the level of acceptable stiffness of such a layer of material will be determined by the requirements placed on the formability, compliance and user comfort of the article. The smallest functional dimension of voids or the like in the storage layer is approximately the size of a drop of water. Consequently, the size of a void or any corresponding space in the acquisition layer should not be so small that a circle with a diameter of 3 mm or more within its boundary edges in the plane of the storage layer.

Short description of the drawings

The invention is described in detail below with reference to the figures of the accompanying drawings. They show:

Fig. 1 is a top view of a diaper according to a first embodiment of the invention, showing an acquisition layer formed by separate bodies of material;

Fig. 2a is a sectional view of the diaper shown in Fig. 1 along the line II-II, before wetting the diaper;

Fig. 2b is a sectional view of the diaper according to Fig. 1, along the line II-TI, after wetting the diaper;

Fig. 3 is a top view of a diaper according to a second embodiment of the invention, and showing an acquisition layer provided with longitudinally extending cavities or channels;

Fig. 4a is a cross-sectional view of the diaper shown in Fig. 3 along the line IV-IV, before wetting of the diaper;

Fig. 4b is a cross-sectional view of the diaper shown in Fig. 3 along the line IV-IV, after wetting of the diaper;

Fig. 5 is a longitudinal sectional view of the diaper shown in Fig. 3 along the line V-V, after wetting of the diaper;

Fig. 6 a diaper with a net-forming storage layer from above;

Fig. 7 shows a detection layer according to the invention with several penetrating openings;

Fig. 8 shows a sensing layer with centrally arranged openings alternating with overlapping material regions;

Fig. 9 a material web for producing a detection layer;

Fig. 10 a detection layer with two rows of openings of different sizes;

Fig. 11 a detection layer with wavy, groove-like cavities;

Fig. 12a and b are enlarged views of an opening and surrounding parts of a dry and wet sample of a first material, respectively; and

Fig. 13a and b are enlarged views of an opening with surrounding parts of a dry and wet sample of a second material, respectively.

The diaper shown in Fig. 1, 2a and 2b is seen from the side thereof which is proximal to the wearer in use. The diaper is shown in a flat expanded state and comprises a first liquid-permeable cover layer 1, for example of nonwoven material, perforated plastic film or net, which on that side of the diaper which, in use, is proximal to the wearer. A liquid-impermeable second cover layer 2, which consists of plastic film, water-repellent nonwoven material or a fabric, is arranged on that side of the diaper which is intended to be distal to the wearer in use. The two cover layers 1, 2 enclose an absorbent body 3 and are connected to one another within parts 4 of the cover layers 1, 2 which project outwards around the absorbent body 3.

The diaper is designed to enclose the lower part of the wearer's body in a panty-like manner when worn. To this end, the diaper comprises a front part 5 which, in use on the wearer, is directed forwards and lies over the wearer's abdomen, a rear part 6 which is intended to be directed rearwards and lies over the wearer's rear part when used on the wearer, and a crotch part 7 which lies between the front diaper part 5 and the rear diaper part 6 and which is intended to be located in the crotch area between the wearer's thighs when used. The diaper has essentially the shape of an hourglass, with the front part 5 and the rear part 6 being wider than the crotch part 7. The diaper further has two longitudinally extending side edges 8, 9 and a front hip edge 10 and a rear hip edge 11. The longitudinal side edges 8, 9 form the leg openings of the diaper in use, while the two hip edges 10, 11 together surround the wearer's hip and form the hip opening of the diaper.

An elastic device 12, 13 is attached along each side edge 8, 9 of the diaper. The elastic devices 12, 13 are attached to the diaper in a stretched state and act to Side edges 8, 9 of the diaper contract as they are relaxed so that the diaper is curved into a tub-like shape. This action of the elastic devices 12, 13 is not apparent from Fig. 1, however, because the diaper is shown in a flat state when the elastic devices 12, 13 are stretched. The elastic devices 12, 13 act to hold the edges of the leg opening of the diaper in tight engagement with the thighs of the wearer. A further elastic device 14 is arranged along the rear hip edge 11 of the diaper such that the edge defining the hip opening is brought into sealing engagement with the hip of the wearer. Several different types of elastic devices 12 to 14 suitable for this purpose are known in the art, such as elastic threads, elastic tapes, elastic webs or similar devices.

With the intention of enabling the diaper to be fastened together in a pant-like form around the wearer's body in use, a fastening tab 15, 16 is provided adjacent each side edge 8, 9 in close proximity to the rear waist edge 11. The fastening tabs 15, 16 are intended to cooperate with and be fastened to a target area 17 provided on the front part 5 of the diaper. The fastening tabs 15, 16 in the normal state have the form of tabs provided with a self-adhesive surface which are folded before use, the adhesive surface being against and protected by a tab area which has been treated with a solvent, or against the diaper itself. The target area 17 consists of a reinforced area of the liquid-impermeable cover layer 2 on the front part of the diaper 5. The simplest way of providing this reinforcement is to attach a strip of plastic film to that side of the liquid-impermeable cover layer 2 which is distal from the absorbent body 3. This reinforcement of the target area 17 enables the diaper to be opened and refastened without tearing the liquid-impermeable cover layer 2.

The fastening tabs 15, 16 may alternatively comprise any kind of mechanical fastening, such as a part of a Velcro-type fastener, a press-stud or a similar fastener. In this case the target area 17 consists of the corresponding part of the mechanical fastening means. It is also known to use fastening means which can be considered almost as hybrids between adhesive fastenings and mechanical fastenings. An example of such a fastening means is described in EP-A-393,953. For diapers intended to be worn as inserts in tight-fitting pants, no fastening means are required.

The absorption body 3 has a first layer, the transport layer 18, which is arranged closest inward from the liquid-permeable cover layer 1. The transport layer 18 is usually made of a soft material which is able to quickly absorb large volumes of liquid and which has comparatively large pores or capillaries for this purpose. Examples of such materials are low-compressed pulp fluff layers, in particular of mechanical, thermomechanical or chemothermo-mechanical pulp (CTMP), chemical pulp consisting of chemically stiffened or cross-linked pulp fibers, or fiber mats and waddings of other types of natural or synthetic fibers. Mixtures of pulp fluff pulp or other pulp-based fibers with different types of synthetic fibers can be used. Soft, perforated or open-cell foam material can also be used. The material preferably has a low liquid spreading ability, whereby the wetness area of the liquid remains essentially limited to the main wetness area, even after repeated wetting of the material. The surface of the diaper which is in contact with the wearer therefore feels dry and comfortable against the skin of the wearer, even after it has been used for a comparatively long time.

When the diaper is in use, the transport layer 18 acts to absorb body fluid and transport it further away from the liquid-permeable cover layer 1 and therefore has relatively large pores which provide the least possible resistance to the flow of fluid. The transport layer 18 is also preferably soft and comfortable against the user's body throughout use. The properties of the material in the transport layer 18 should preferably not change appreciably after wetting. It is also desirable that the material have a certain degree of flexibility so that the material tends to return to its original state after being compressed or crumpled during use.

If the transport layer 18 comprises cellulose fibres which usually have a comparatively low compliance when wet, for example chemical pulp, it may be appropriate to mix in other material which improves the wet compliance of the material and thereby gives the first absorption layer a certain compliance even when the layer is wet. Such materials are, for example, different types of thermoplastic fibres or particles which, when the layer is heated, act to bond the fibres in the layer and thereby change their relative positions. such that the layer has a higher tensile strength on the one hand and a higher compliance in both a wet and a dry state on the other hand. The pulp fibers can also be chemically modified by cross-linking, for example, such that their intrinsic compliance is improved, or by blending the pulp fibers with highly compliant synthetic fibers.

The transport layer 18 may further comprise a small amount of so-called superabsorbents, i.e. material in the form of fibers, particles, granules, films or the like, which is capable of chemically absorbing and binding body fluid in an amount that corresponds to a multiple of the intrinsic weight of the superabsorbent, while forming a hydrogel.

Disposed within the transport layer 18, viewed in a direction from the liquid-permeable cover layer 1, is a second absorbent layer 19, hereinafter referred to as the acquisition layer, which is intended to rapidly absorb and collect comparatively large volumes of body fluid. The acquisition layer 19 consists of a plurality of cylindrical bodies 20, each having a planar surface 21 in engagement with the transport layer 18 and its other planar surface 22 in engagement with a third absorbent layer, the storage layer 23, disposed within the acquisition layer 19, closest to the liquid-impermeable cover layer 2. The cylindrical bodies 20 are arranged in a spaced-apart relationship leaving between them a coherent cavity or space 24 in which body fluid discharged onto the diaper can be collected. The liquid acquisition space 24 may alternatively consist of a space of lower density and basis weight than surrounding material parts and may for example, comprise a porous, resilient material such as a fiber wadding, an absorbent foam or a similar material. Material may also extend from the transport layer 18 into the space 24.

As can be seen from the diaper shown in Fig. 1, the main extension of the diaper lies in the xy-plane, the x-direction being defined by the transverse direction of the diaper, and the y-direction being defined by the longitudinal direction of the diaper. The cylindrical bodies 20 are made of a material which, when wetted with body fluid, expands extensively in the z-direction, i.e. in the direction perpendicular to the xy-plane, and only expands to a small extent in the xy-plane, such that the volume of the fluid acquisition space (24) increases by at least 100%, preferably at least 200%, and more preferably at least 500% when the material is saturated with a 0.9% NaCl solution. The expansion of the material in the xy direction is preferably no greater than an amount that reduces the area of the space 24 in the xy direction by at most 25%, preferably at most 20%, and most preferably at most 10% when the material is wetted to saturation according to the foregoing. An expansion of the material in the z direction is preferably at least 100%, preferably at least 200%, and most preferably at least 500% when it is wetted to saturation according to the foregoing.

Suitable materials for this purpose are, for example, pulp fibres from mechanical, thermomechanical, chemomechanical or chemothermomechanical pulp (CTMP) and/or chemical pulp fibres which have been chemically stiffened or cross-bonded, the fibres being formed into a web having a basis weight of 30-2000 g/m², preferably 50-1500 g/m² and most preferably 100-1000 g/m², and to a density of between 0.2-1.2 g/cm³, preferably 0.25-1.0 g/cm³ and most preferably between 0.3-0.9 g/cm³. The production of a particularly suitable material of this type is described in WO94/10956. A characteristic feature of this material is that it is produced by dry forming flake dried pulp fibers into a web having a basis weight of 30-2000 g/m² and compressed to a density of between 0.2-1 g/cm³.

Another suitable expansion material is compressed cellulose fluff pulp (density at least 0.2 g/cm3) mixed with a certain amount of superabsorbent material, albeit less than 20 wt% superabsorbent material. The admixture of superabsorbent material will in fact lead to an increase in the extent to which the material swells in the xy-direction, i.e. the area of the space 24 will decrease. However, the material used according to WO94/10956 allows a larger amount of superabsorbent material to be mixed with the material, since the material swells very extensively in the z-direction, which compensates for the swelling in the xy-direction.

The materials described above are often manufactured in relatively thin sheets that are only a few millimeters thick. The cylindrical bodies can be formed from one or more layers of such a material.

Other suitable materials for the cylindrical bodies are compressed foam materials or fibre wadding which will at least partially return to their uncompressed size when wetted. If required, the materials can be locked in their compressed state with the aid of some form of water-soluble binding agent. The above examples of suitable wet-expanding materials are for the are intended to clarify the invention and should not be considered as limiting its scope.

The third layer 23 of the absorbent body, hereinafter referred to as the storage layer, consists of a material having a high liquid acquisition and storage capacity. A suitable material in this respect is cellulose fluff pulp having a density of between 0.08-1.0 g/cm³, preferably 0.1-0.6 g/cm³, in combination with 2-80%, preferably 10-50% superabsorbent material, calculated on the total weight of the layer in a dry state. The superabsorbent material may be in the form of flakes, granules, powder or the like, and is mixed with the cellulose fibers or applied in the form of one or more layers between the fiber layers. The superabsorbent material is either uniformly distributed in the storage layer 23 or with varying concentrations in the xy-direction or the z-direction of the storage layer. The superabsorbent material can alternatively be in the form of a film.

The storage layer 23 can conceivably consist of a layer consisting essentially of a superabsorbent material. Absorbent foam material, tissue laminate with superabsorbent material and dry-formed, flak-dried pulp fiber layers according to WO94/10956, optionally mixed with superabsorbent material, can also be used as storage layers.

The fourth layer 25 of the absorbent body, hereinafter referred to as the liquid distribution layer, may according to a first alternative comprise a material of high density and with an extensive ability to distribute or spread the liquid through capillaries. Suitable materials in this In this respect, compressed layers of cellulose fluff pulp, tissue, absorbent foam material or dry-formed, flake-dried cellulose fiber layers according to WO94/10956 are suitable. The distribution layer 25 is preferably free of superabsorbent material or contains only a small amount of a superabsorbent material. The layer preferably has a smaller extension in the xy plane of the diaper than the transport layer 18. The liquid distribution layer is thereby surrounded on all sides by a soft, body-friendly material with low liquid distribution capacity.

The distribution layer 25 may conveniently be provided with a longitudinally extending compression pattern, such as grooves, corrugations or the like, effective to direct liquid transport in the longitudinal direction of the diaper.

According to a second alternative, the liquid distribution layer 25 is made of a material which has a low resistance to liquid flow, so that the liquid is allowed to spread or distribute relatively freely along the layer. Suitable materials in this respect are a porous fiber mat or wadding made of synthetic or natural fibers or an open-cell foam material. The main purpose of the liquid distribution layer 25 is to transport body fluid away from the area of the diaper which first absorbs body fluid, i.e. the main wet area. This results in a better use of the absorbent material in the absorbent body 3. The liquid distribution layer 25 can be arranged either between the acquisition layer 19 and the storage layer 23 (shown with a dotted line in Fig. 2a) or, as described above, between the storage layer 23 and the liquid-impermeable outer cover layer 2.

The cylindrical bodies 20 in the acquisition layer 19 are preferably attached, e.g. glued, to the underlying storage layer 23 or the distribution layer 25, so that the cylindrical bodies 20 are prevented from moving within the diaper. Alternatively, the cylindrical bodies 20 may be attached to a separate layer, e.g. a tissue or nonwoven layer, or they may be attached to the liquid transport layer 18. Of course, the cylindrical bodies 20 may be attached to more than one layer.

All absorption layers 18, 19, 23, 25 in the absorption body 3 are in direct liquid communication with one another. Thus, liquid is continuously transported into the liquid acquisition layer 19 of the diaper in a direction generally perpendicular to the cover layer 1, regardless of where liquid impacts the liquid-permeable cover layer 1 of the diaper.

As can be seen from Fig. 2a, the liquid acquisition layer 19 is comparatively thin before the diaper has absorbed body liquid. However, the cavity 24 formed between the cylindrical bodies 20 on the diaper shown in Fig. 2a is sufficient to accommodate a first volume of discharged liquid. The discharged body liquid impinges on the liquid-permeable cover layer 1 of the diaper within a small, limited area or region, the so-called main wet area.

The position of the main wetness area in the diaper will vary slightly between different users. This is due to differences in body shape on the one hand and the gender of the user on the other. Male users tend to place a diaper slightly further forward. wet than a female user. The position of the main wetting area in a diaper may also vary with respect to one and the same user during use as a result of changes in body movement and postures. It is thus not necessary to determine the exact position of the wetting area of the diaper shown. However, the main wetting area is somewhere in the crotch portion 7 of the diaper.

Liquid that has passed through the transport layer 18 is collected in the cavity 24 between the cylindrical bodies 20 of the acquisition layer 19 and in the fiber structure closest to the main wetting area of the diaper. The liquid is then spread in the xy plane of the diaper by the absorbent material in the distribution layer 25.

However, a portion of the liquid collected in the cavity 24 in the acquisition layer 19 at the first wetting event is absorbed by the cylindrical bodies 20. Because the material of the cylindrical bodies 20 expands in the z-direction of the diaper when it is wetted, the expansion of the transport layer 18 and the storage layer 23/liquid distribution layer 25 causes them to separate in the z-direction, thereby enlarging the cavity 24. Thus, at the next diaper wetting event, the space available for immediate liquid acquisition becomes larger than at the first wetting event. The rate at which liquid penetrates the diaper therefore does not decrease to any appreciable extent, or may even increase upon repeated wetting of the diaper absorbent body 3.

Since the space 24 in the liquid capture layer 19 between the cylindrical bodies is coherent, liquid penetrating through the transport layer 18 is distributed over a comparatively large area around the main wet area out. Liquid is absorbed comparatively slowly in the storage layer 23 and the distribution layer 25 due to the compact structure of these layers, whereby a large part of the liquid is able to run onto the surface of the layer 23 facing the space 24 and thereby spread over a considerable area before being absorbed by the storage layer 23 or by the cylindrical bodies 20 in the acquisition layer 19. Thus, it is not only the cylindrical bodies 20 located closest to the main wetting area that are wetted by the liquid and swell in the z-direction, but such expansion will also be observed to occur at a distance from the wetting area. The liquid gradually spreads further into the diaper, by means of the liquid transport in the distribution layer 25, for further storage in the storage layer 23.

The diaper shown in Figures 3 to 5 is of substantially the same construction as the diaper in Figure 1 and comprises an absorbent body 103 enclosed between a liquid-permeable cover layer 101 and a liquid-impermeable cover layer 102. The diaper comprises a front part 105, a rear part 106 and an intermediate crotch part 107 and has two longitudinally extending side edges 108, 109, a front waist edge 110 and a rear waist edge 111. The diaper is substantially T-shaped, with the transverse element of the T forming the front part 105 of the diaper, the vertical element of the T gradually increasing in width from the crotch part 107 of the diaper over the rear part 106 and towards the rear waist edge 111.

Elastic devices 112, 113 are arranged along the side edges 108, 109 of the diaper in a V-shaped pattern, and diverge from the front hip edge 110 towards the rear hip edge 111. A Fastening tab 115, 116 is disposed on each side edge 108, 109 on the rear portion 106 proximate the rear waist edge 111, and a corresponding target region 117 is disposed on the outside of the liquid impermeable cover layer 102 on a front portion 106 of the diaper proximate the front waist edge 110.

The absorbent body 103 of the diaper comprises a liquid transport layer 118 of the same type as that of the diaper according to Fig. 1 and of the same format as the size of the diaper. A liquid acquisition layer 119 with elongated liquid acquisition spaces or channels 124 is arranged within the transport layer 118. As can be seen from Fig. 3, the channels 124 can extend in the longitudinal direction of the article or alternatively in its transverse direction. The channels 124 can either consist of hollows punched out in the acquisition layer 119 or alternatively an acquisition layer 119 can consist of several layers of longitudinally extending or transversely extending strips between which elongated liquid acquisition spaces or channels 124 are arranged. The strips are attached to a storage layer 123 or a liquid distribution layer 125 of a type and size corresponding to those of the diaper shown in Fig. 1, for example by gluing or some other way. As in Fig. 2a, Fig. 4a shows the alternative positions of the liquid distribution layer 125. A dotted line indicates the position above the storage layer 123 and a continuous line indicates the position below the storage layer 123. In Figs. 4b and 5 only the second alternative is shown.

As best seen in Fig. 4a, the channels 124 in the acquisition layer 119 are relatively flat before the diaper is wetted. However, the volume of the channels 124 sufficient for the diaper to absorb a first volume of liquid. The liquid entering the diaper is able to flow rapidly away from the main wetting area along the channels 124. The liquid from the channels 124 is then gradually absorbed by the acquisition layer 119, the storage layer 123 and the distribution layer 125, respectively. Of course, a portion of the liquid drained to the diaper and penetrating downward through the transport layer 118 will immediately wet those parts of the acquisition layer 119 located in the main wetting area of the diaper, which parts of the acquisition layer will immediately begin to swell in the z-direction of the diaper. Wetting of the acquisition layer 119 at a distance from the main wetting area only takes place after a given time delay required for the liquid to leak into the channels 124. Fig. 5 shows how liquid is spread in the lengthwise direction of the diaper as a result of the varying extent of expansion of the acquisition layer 119 (shown in sections) in the z-direction of the diaper depending on the distance from the main wetting area. Fig. 4b is a similar illustration to illustrate the distribution of liquid in the cross-direction of the diaper.

The diaper shown in Fig. 6 has generally the same construction as the diapers shown in Figs. 1 to 5 and comprises an absorbent body 203 enclosed between a liquid-permeable cover layer 201 and a liquid-impermeable cover layer 202. The diaper has generally an hourglass shape and comprises a front part 205, a rear part 206, a narrower intermediate crotch part 207, two longitudinally extending side edges 208, 209, a front waist edge 210 and a rear waist edge 211. The elastic devices 212, 213 are arranged along the longitudinally extending side edges 208, 209 of the diaper and disposed along the rear waist edge 211. The diaper is secured together in a pant-like configuration by means of two fastening tabs 215, 216 disposed on the longitudinally extending side edges 208, 209 proximate the rear waist edge 211. The fastening tabs may be secured to a target area 217 on the front portion 205 of the diaper proximate the front waist edge 210.

The absorption body 203 consists of two layers 219, 223. The absorption layer 219, the acquisition layer 219, which is arranged closest to the liquid-permeable cover layer 201, consists of a coarse-mesh, knitted, braided or woven net 226 of material that swells in the thickness direction of the diaper, i.e. in the z-direction, when wetted. The material can, for example, be made of threads, ribbons or strips comprising a superabsorbent, gel-forming material. Another conceivable material is threads or ribbons coated with a polymer mixture that ferments when wetted to form a stable foam on the ribbons or threads. Below the acquisition layer 219, viewed in a direction away from the liquid permeable cover layer 201, there is arranged a storage layer 223 of the same type as that described with reference to the diapers shown in Figs. 1 to 5. Of course, the diaper shown in Fig. 6 can also be provided with a soft, coarse-pored liquid acquisition transport layer between the liquid permeable cover layer 201 and the storage layer 219 if desired. Similarly, a liquid distribution layer can be arranged in a manner corresponding to that described with reference to Figs. 1 to 5.

Fig. 7 shows an alternative embodiment of a liquid acquisition layer 219 made of a material that can swell in the z-direction. The acquisition layer 319 has a plurality of penetrating circular openings or spaces 324 that act as liquid-storing reservoirs. The acquisition layer 319 is intended to be used as the sole absorbent layer, or together with other absorbent layers, such as liquid transport layers, storage layers, and/or distribution layers in an absorbent article, such as a diaper, sanitary napkin, incontinence guard, or similar article. Because the acquisition layer swells in the z-direction, i.e. in the thickness direction, when it is wetted, the volume of the openings 324 will increase and thus its liquid absorption capacity will also increase.

The highest proportion of voids 324 in the acquisition layer 319 is located in the area intended to be located in the main wetting area of the absorbent article. Since the openings 324 are not connected to each other, liquid is not able to flow freely between the openings, but is distributed in the xy plane of the acquisition layer 319 by capillary transport in the absorbent material located between the openings 324. Consequently, there is no apparent reason to provide openings 324 at too great a distance from the main wetting area.

Fig. 8 shows a further embodiment of an acquisition layer 419 for use in absorbent articles. The acquisition layer according to Fig. 8 is formed from a web of material which is cut into two pieces in the longitudinal direction along an arcuate curve 427, whereupon the two web halves 428, 429 are bent relative to each other in the longitudinal direction of the web by a distance corresponding to half a wavelength. Thus, a longitudinally extending central portion of track openings 424 is formed, alternating with overlapping track portions 430. As in the previously described embodiments, the sensing layer 419 is made of a material that swells in the thickness direction of the material, ie, in the z-direction, when wetted.

In Fig. 9, an example of another sheet material is shown which is provided with apertures 524 and is formed by first cutting the sheet 519 longitudinally into two parts in a curved pattern, after which the separated parts of the sheet have been offset longitudinally so as to produce a repeating pattern of apertures 524 and overlapping parts 530 in the sheet. The sheet 519 shown in Fig. 9 has been cut longitudinally along two generally sinusoidal curves 527. After offsetting the edge parts 528, 529 of the sheet with respect to its central part 531, two longitudinally extending rows of apertures 524 with overlapping parts 530 therebetween are obtained. Of course, the principle can be used to provide any desired number of rows of openings in a web of material. In this respect, the number of rows of openings is determined by the number of curved-shaped cuts made in the web.

The web 619 shown in Fig. 10 was cut in the longitudinal direction in the same way as the web 519 according to Fig. 9. One edge portion 628 of the web 619 was offset longitudinally and transversely from the longitudinal centerline 632 of the web 619. The other edge portion 629 was offset both longitudinally and transversely toward the longitudinal centerline 632 of the web 619. This allows the size of the openings 624', 624" and the size of the overlapping portions 630', 630" to be adjusted. The size of the openings 624" can be reduced by offsetting an edge portion 629 toward the longitudinal centerline 632 of the web 619 while at the same time obtaining greater overlap 630" between the web portions, the size of the openings 624 is increased in a corresponding manner by offsetting the edge portion 628 of the web 619 away from the centerline 632.

Fig. 11 shows the manner in which coherent, longitudinally extending openings can be obtained between parts of the material web 719 that have been cut apart along generally sinusoidal curves 727. The web parts 728, 729, 731 according to Fig. 11 are offset from each other in both the longitudinal and transverse directions of the web 719 by moving the cut edge parts 728, 729 laterally away from the longitudinal centerline 732 of the web 719. The width of the coherent openings 724', 724" between two web parts is determined by the distance by which the web parts are separated. Fig. 11 shows two examples of openings of mutually different widths 724', 724". Of course, the track 719 can be provided with any number of coherent openings of the type described.

The web members may be arranged in the article such that the curved cuts or slits are arranged in either the longitudinal or transverse direction of the article. Curve shapes other than sinusoidal curves may be chosen, such as sawtooth shapes or square wave shapes.

Varying sizes can be obtained with waves having different amplitudes along the curve, for example such that the openings located in the wet area are larger than the openings located outside this area. Waves of varying wavelengths can also be chosen, thereby providing a varying overlap between the openings obtained for a given offset between the track parts.

Examples

Samples measuring 5 x 5 cm were punched from sample material with the following components:

A) DFR (dry formed roll pulp), i.e. a dry formed pulp layer made of flak dried cellulose fibres from CTMP (according to WO94/10956); basis weight 300 g/m².

B) DFR according to the above, with 20 wt.% of a superabsorbent material (Salsorb CL10) admixed.

C) Chemical cellulose fluff pulp to which 48% by weight of a superabsorbent material (IM 7100) has been added, basis weight 500 g/m².

D) Chemical cellulose fluff pulp mixed with 30% by weight of a superabsorbent material (IM 7100), basis weight 300 g/m².

Four circular holes measuring 10 mm in diameter were punched out of each sample.

The samples were weighed in a dry state and their thickness was measured with a 45 x 45 mm measuring instrument at a pressure of 2.5 N.

The samples were placed on a dense mesh material (a tea bag-like material) and allowed to swell freely in a dish containing a 0.9% NaCl solution.

The samples were then removed from the tray and allowed to drain for approximately 30 seconds, after which the wet thickness was measured and the sample was weighed.

The difference between the wet and dry thickness determines the swellability of the material in its z-direction.

The following results were obtained: Table 1

The measurement results represent the average of four measurements.

With the intention of measuring the swelling in the xy direction, and to measure the influence of the swelling on the size of the openings, an image analysis was carried out using the programs Image Grabber and Optilab as follows:

Examples according to the above were arranged in a small glass dish.

A dark paper was placed on the light table of the image analysis device, and the glass dish and the sample were placed on the paper.

The Image Grabber program was opened and the camera was focused. Four images were taken of the wet sample from directly above, one for each aperture.

A 0.9% NaCl solution was carefully poured into the dish and the sample was allowed to freely absorb liquid for 20 minutes.

Excess fluid was carefully removed with a pipette.

Four images were taken from directly above the wet sample, one for each aperture. Figures 12a and 12b show an aperture with surrounding parts of a dry and wet sample piece of Sample A, respectively.

Fig. 13a and b show an opening with surrounding parts of a dry and a wet sample piece of sample C, respectively.

As can be seen from the pictures, the opening in specimen A has a substantially maintained area after wetting, while the opening area of specimen C has significantly decreased.

The size (area) of the opening was measured as follows:

A dry scale image was made by placing a Vernier caliper set at 10.0 mm on the dry sample, after which an image was taken in the image grabber.

A wet scale image was taken by placing a Vernier caliper set to 10.0 mm on the wet sample and then taking an image in the Image Grabber.

The Optilab program (Graftek) was opened for calibrating the scale. A line was drawn on the calibration image, which was calibrated to 10.0 mm.

Each opening to be measured was calibrated against the scale image of the respective sample.

The grey scale at the edge of the aperture was measured, i.e. the line of distinction between greyish and grey (cf. Fig. 13b), where black is the aperture, grey is the superabsorbent material, and greyish is the colour of the pulp.

The opening area was marked in millimeters and the result was printed out.

The following results were obtained: Table 2

The measured values represent the average of four measurements. The opening volume was calculated as the product of the opening area and the sample thickness (see Table 1).

The results obtained for samples C and D clearly show that the requirement that the sensing layer material should increase in size in the z-direction is not sufficient to ensure a significant increase in the volume of the liquid sensing space. In fact, sample C, with an increase in size in the z-direction of 148%, results in a volume increase of only 1%. Sample D is only slightly better. Thus, the requirement according to the present invention that the sensing layer material must also show a comparatively small expansion in the xy-direction when wetted is essential.

Although the invention has been described above generally with reference to diapers, it will be appreciated that the invention is applicable to all types of absorbent articles intended to absorb body fluid. Examples of such articles are diapers and incontinence guards for children and adults, sanitary napkins, panty liners, bed protectors, seat protectors, wound dressings and similar articles.

It is further to be understood that the invention is not limited to the described shapes and sizes of openings, channels and swellable bodies, and that a number of further embodiments are conceivable. For example, openings arranged in a liquid acquisition layer may have any other shape or size. It is of course also possible to combine openings and channels of different sizes and shapes in one and the same article. Swellable bodies arranged as "columns" in a coherent cavity may also vary in size and shape and are not limited to the cylindrical bodies described above. As mentioned above, the liquid acquisition cavities may consist of a space whose density and basis weight are lower than the density and basis weight of the surrounding absorption layer and can, for example, comprise a porous, flexible material such as a fiber wadding, an absorbent foam material or the like.

An absorbent body can also have more than one acquisition layer. In this regard, further acquisition layers can be of the same type as the first acquisition layer or can differ from it by means of the choice of material or the structure.

Claims (22)

1. An absorbent article comprising a liquid-permeable outer cover layer (1) arranged on a first surface of the article, a liquid-impermeable cover layer (2) arranged on a second surface of the article, and an absorbent body (3) enclosed between the two cover layers and comprising a liquid acquisition layer (19) and, arranged substantially in the same plane therewith, a liquid acquisition space (24) comprising at least one cavity or at least one region of lower density than the liquid acquisition layer (19) adjacent to the space (24), and wherein the acquisition layer (19) comprises a material which, when wetted, increases in size in a direction (z-direction) generally perpendicular to the first surface of the article, characterized in that the material in the acquisition layer (19) when wetted has a comparatively small expansion in a direction (xy direction) generally parallel to the first surface of the article such that the volume of the liquid-acquisition space (24) increases by at least 100% when the material is wetted to saturation with a 0.9% NaCl solution. 2. Absorbent article according to claim 1, characterized in that the volume of the liquid acquisition space (24) increases by at least 200%, preferably at least 400% and most preferably at least 900%. 3. Absorbent article according to claim 1 or 2, characterized in that the expansion of the material in the xy-direction is not greater than that it leads to a reduction of the area of the liquid acquisition space (24) in the xy-direction by at most 25%, preferably at most 20% and most preferably at most 10% when it is wetted to saturation with a 0.9% NaCl solution. 4. Absorbent article according to one or more of the preceding claims, characterized in that the expansion of the material in the z-direction is at least 100%, preferably at least 200%, even more preferably at least 400% and most preferably at least 900% when it is wetted to saturation with a 0.9% NaCl solution. 5. Absorbent article according to one or more of the preceding claims, characterized in that a storage layer (23) in liquid connection with the acquisition layer (19) is arranged on that side of the acquisition layer which is proximal to the liquid-impermeable cover layer (2). 6. Absorbent article according to claim 5, characterized in that the storage layer (23) comprises a material that has good liquid-holding properties, such as cellulose fibers in combination with superabsorbent material, tissue laminates with superabsorbent material or absorbent foam material. 7. Absorbent article according to claim 5 or 6, characterized in that a liquid distribution layer (25) is arranged in liquid communication with the acquisition layer (19) either between the acquisition layer and the storage layer (23) or between the storage layer and the liquid-impermeable cover layer (2). 8. Absorbent article according to claim 7, characterized in that the distribution layer (18) comprises a material that has good liquid distribution properties, such as compressed cellulose pulp, a porous fiber mat or padding of synthetic or natural fibers or an open-cell foam material. 9. Absorbent article according to one or more of the preceding claims, characterized by a liquid transport layer (18) arranged between the liquid-permeable cover layer (1) and the liquid acquisition layer (19). 10. Absorbent article according to claim 9, characterized in that the transport layer (18) comprises a material that is able to rapidly absorb liquid and to pass the liquid on to underlying layers and can consist, for example, of a slightly compressed cellulose fluff layer of mechanical, thermomechanical or chemithermomechanical pulp (CTMP), chemically stiffened or cross-linked cellulose fibers or a fiber mat or padding made of synthetic or natural fibers or an absorbent foam material. 11. Absorbent article according to one or more of the preceding claims, characterized in that the liquid acquisition space (24) consists of one or more openings extending through at least parts of the thickness of the acquisition layer (19) or regions of lower density than the surrounding material (20, 125) in the acquisition layer (19). 12. Absorbent article according to one or more of claims 1 to 10, characterized in that the acquisition layer (19) consists of at least two separate material bodies (20) which extend as columnar spacing devices generally vertically between two further material layers (18, 23) in the article and together with the material layers (18, 23) define a coherent liquid acquisition space (24) between the material layers (18, 23). 13. Absorbent article according to one or more of claims 1 to 10, characterized in that the liquid acquisition space (124) consists of at least one channel (124) extending in the longitudinal direction of the article. 14. Absorbent article according to one of claims 1 to 10, characterized in that the acquisition layer (19) is formed by a material web which has been divided in the longitudinal direction of the web along a wavy curve which crosses at least twice a line extending in the longitudinal direction of the web; and in that the web parts are offset with respect to each other in the plane of the web at least in the longitudinal direction of the web, wherein the Track parts therebetween define the liquid collection space (24) in the plane of the track. 15. Absorbent article according to claim 14, characterized in that the material web is arranged in the article so that the wavy curve extends either in the longitudinal direction of the article or in the transverse direction thereof. 16. Absorbent article according to one or more of the preceding claims, characterized in that the acquisition layer (19) consists of pulp fibers of mechanical, thermomechanical, chemimechanical or chemithermomechanical pulp (CTMP) and/or chemical pulp fibers which have been chemically stiffened or cross-linked, the fibers being formed into a web with a basis weight of 30-2000 g/m², preferably 50-1500 g/m² and more preferably 100-1000 g/m², and compressed to a density of between 0.2-1.2 g/cm³, preferably 0.25-1.0 g/cm³ and most preferably 0.3-0.9 g/cm³. 17. Absorbent article according to claim 16, characterized in that the pulp fibers consist of fluff-dried fibers which have been dry-formed into a web and have been incorporated into the article without defibration and fluff formation. 18. An absorbent article according to any one of claims 16 or 17, characterized in that the acquisition layer (19) consists of an airlaid web of pulp fibers which has been compressed into a dry-formed layer having a first density of between 0.2-1.2 g/cm³ and which has then been mechanically softened to a second density which is lower than the initial density, and has been delaminated in such a way that a plurality of not completely separated thin fiber layers are formed which have a density corresponding to the first density. 19. Absorbent article according to one of the preceding claims, characterized in that the acquisition layer (19) consists of a material layer having a first thickness and comprising compliant material, the material layer having been compressed to a second thickness perpendicular to a plane through the layer and in its compressed state having been bonded to a binding agent which is soluble in body fluid, the bonding of the material layer disappearing when the layer is wetted and the acquisition layer (19) at least partially returning to its first thickness. 20. Absorbent article according to claim 19, characterized in that the acquisition layer (19) consists of a compressed foam material which expands in its thickness direction when wetted. 21. Absorbent article according to claim 19, characterized in that the acquisition layer (19) consists of a compressed fiber layer which at least partially comprises fibers with a certain compliance in the wet state. 22. Absorbent article according to one or more of the preceding claims, characterized in that the portion of the volume of the acquisition layer (19) consisting of the liquid acquisition space (24) is greatest within the main wetting area of the article, that is, the area of the article which is intended to be initially wetted by body fluid.